Ensure backwards compatibility for GetStableLatestTransactionId()

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 1654a0e5c739e56f742ad094fd422633d8896c9d..c71a10e4ea21fbeee273f6f8065b29b3312609ae 100644 (file)
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -390,11 +390,10 @@ GetCurrentTransactionIdIfAny(void)
    return CurrentTransactionState->transactionId;
 }
 
-
 /*
- * GetStableLatestTransactionIdIfAny
+ * GetStableLatestTransactionId
  *
- * Get the latest XID once and then return same value for rest of transaction.
+ * Get the XID once and then return same value for rest of transaction.
  * Acts as a useful reference point for maintenance tasks.
  */
 TransactionId
@@ -403,13 +402,16 @@ GetStableLatestTransactionId(void)
    static LocalTransactionId lxid = InvalidLocalTransactionId;
    static TransactionId stablexid = InvalidTransactionId;
 
-   if (lxid != MyProc->lxid ||
-       !TransactionIdIsValid(stablexid))
+   if (lxid != MyProc->lxid)
    {
        lxid = MyProc->lxid;
-       stablexid = ReadNewTransactionId();
+       stablexid = GetTopTransactionIdIfAny();
+       if (!TransactionIdIsValid(stablexid))
+           stablexid = ReadNewTransactionId();
    }
 
+   Assert(TransactionIdIsValid(stablexid));
+
    return stablexid;
 }